1. Field of the Invention
The present invention relates to a flame retardant hydraulic oil to be used in rolling mills, die casting machines and the like in the fields of the steel making industry and the nonferrous metal industry and in hydraulic instruments and the like in the construction industry. More particularly, it relates to a flame retardant hydraulic oil excellent in the flame retardancy, unaccompanied by the dangers of pinhole fire at sites of use and giving rise to no environmental contamination.
2. Description of the Related Arts
Generally, it is essential that the flame retardant hydraulic oils have the following characteristics:
(1) they are excellent in viscosity-temperature properties to ensure the transmission of pressure and power,
(2) they have appropriate viscosities to minimize the loss of pressure and power,
(3) they are excellent in the heat stability, oxidative stability and lubricity to provide the longer service life,
(4) they are excellent in the demulsibility to protect from the possible mixture of water, and
(5) they have flash points high enough not to permit the continuous burning even if they are ignited, since it is quite likely that they are used where there are high risks of fire.
As the flame retardant hydraulic oils, there have been conventionally used those of emulsion series, those of water-glycol series, those of phosphoric acid ester series and those of fatty acid ester series
However, the hydraulic oils of emulsion series and those of water-glycol series are short on the heat stability, oxidative stability and lubricity, accompanied by the difficulty to dispose of waste water containing the oils. Furthermore, the hydraulic oils of phosphoric acid ester series have the shortcomings that their viscosity-temperature properties and hydrolytic resistance are deficient; they are responsible for the deterioration of seal materials and the exfoliation of coats; and it is not easy to dispose of waste water oil by burning.
On the other hand, the hydraulic oils of fatty acid ester series are good in all of the above points and have found their application in wide segments of market. But they have the shortcomings in that they are low in the fire resistance and flame retardancy. Various studies have been conducted in an attempt to find the solution in the problems incidental to the hydraulic oils of fatty acid ester series. In fact, the technique covering the flame retardant hydraulic oils of fatty acid ester series has been disclosed, for example in Japanese Patent Applications Laid Open No. 18467/1980, No. 226096/1984, No. 125598/1988, No. 214795/1990 and No. 21697/1991.
However, all of those disclosed in said patent applications have the flame retardancy defined in terms of flash point. The most important problem of flame retardant hydraulic oils is accidents caused by pinhole fire. Specifically speaking, the flame retardant hydraulic oils should have the properties that they are hard to catch fire even if they are erupted from pinholes and, even in the case of catching fire, do not permit the oil to develop into the continuous burning if the source of fire is removed. These properties cannot be obtained merely by having high flash points alone.
The present inventors have taken note of said properties of continuous burning and conducted the studies by spraying and burning various flame retardant oils under high pressure. The studies have resulted in the finding that even the conventional flame retardant oils of fatty acid ester series do not have the fully satisfactory flame retardancy, although they are highly spoken of as flame retardant.
Thus, the present inventors have made the further intensive studies with a view to developing a flame retardant hydraulic oil of fatty acid ester series free from the properties of continuous burning. As the results, it has been found that the desired flame retardancy is provided by a specific partially esterified product having a molecular structure with hydroxyl groups. The present invention has been completed on the basis of this finding.
Among other patents, said Japanese Patent Application Laid Open No. 125598/1988 describes that an increase in the number of hydroxyl groups in the fatty acid esters is not preferable because such an increase causes their flash point to lower and that the hydroxyl value of 30 mg KOH/g or less is preferable. However, the present inventors have found from their own studies that a compound having the hydroxyl value of 35 mg KOH/g or more exhibits the good flame retardancy. The present invention has been completed on the basis of this finding.
Accordingly, an object of the present invention is to provide a flame retardant hydraulic oil containing a hydraulic base oil comprising a polyol partial ester which is a product formed by reacting (A) a polyol having a total of 3 to 12 carbon atoms and a total of 3 to 6 hydroxyl groups with (B) acyclic monocarboxylic acid having a total of 6 to 22 carbon atoms, said polyol partial ester having a hydroxyl value of 35 mg KOH/g or more, a flash point of 290xc2x0 C. or higher and an average molecular weight of 600 to 1,500.
The present invention will be described in greater detail below.
The flame retardant hydraulic oils of the present invention contain a hydraulic base oil comprising a fatty acid ester as the essential component. The fatty acid esters of the present invention are an polyol partial ester obtained by reacting a polyol of Component (A) with an acyclic monocarboxylic acid of Component (B).
The polyols of Component (A), which are used in the esterification to form the polyol partial esters, are polyols having a total of 3 to 12 carbon atoms and a total of 3 to 6 hydroxyl groups. Their specific examples include a trihydric alcohol such as glycerin, trimethylolethane, trimethyolpropane and trimethyolnonane; and a polyhydric alcohol such as pentaerythritol, ditrimethylolpropane, dipentaerythritol, sorbitol and mannitol. Of them, the trimethylolpropane, pentaerythritol and glycerin are preferably used. These polyols can be used singly or in their two or more mixture.
The acyclic monocarboxylic acids of Component (B), which are used in the esterification to form the polyol partial esters, are monocarboxylic acids having a total of 6 to 22 carbon atoms. Their specific examples include a straight chain saturated fatty acid such as caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, arachic acid and behenic acid; a straight chain unsaturated fatty acid such as undecenoic acid, oleic acid, elaidic acid, cetoleic acid, erucic acid and brassidic acid; and a branched chain saturated fatty acid such as isomyristic acid, isopalmitic acid, isostearic acid, 2,2-dimethylbutanoic acid, 2,2-dimethylpentanoic acid, 2,2-dimethyloctanoic acid, 2-ethyl-2,3,3-trimethylbutanoic acid, 2,2,3,4-tetramethylpentanoic acid, 2,5,5-trimethyl-2-t-butylhexanoic acid, 2,3,3-trimethyl-2-ethylbutanoic acid, 2,3-dimethyl-2-isopropylbutanoic acid, 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid. These acyclic monocarboxylic acids can be used singly or in their two or more mixture.
According to the present invention, the hydraulic base oils of flame retardant hydraulic oil comprise as the essential component the polyol partial esters formed by using the polyols of Component (A) and the acyclic monocarboxylic acids of Component (B) respectively singly or in a mixture of two compounds or more and subjecting them to the ordinary esterification.
In the processes wherein the polyols of Component (A) and the acyclic monocarboxylic acids of Component (B) are subjected to the esterification, the ratio of the charge of Component (A) to that of Component (B) can be adjusted to obtain the polyol partial esters having the hydroxyl value as desired. Furthermore, it is preferable to remove fractions of light components to perfection, to provide the flash point of 290xc2x0 C. or higher.
The thus obtained esterification products can be employed either singly as they are or by mixing them to provide the viscosity as desired upon their use as the polyol partial esters in the hydraulic base oils.
According to the present invention, the esterified polyol portions to be used in the hydraulic base oil have a hydroxyl value of 35 mg KOH/g or more, preferably 50 mg KOH/g or more, more preferably 70 mg KOH/g or more. The hydroxyl value of less than 35 mg KOH/g is not preferable because it leads to an increase of completely esterified portions and the resultant hydraulic oils are undesirably as much susceptible to the continuous burning as those conventionally available. Furthermore, it is preferable that flash points be 290xc2x0 C. or higher. If the flash points are lower than 290xc2x0 C., the hydraulic oils are liable to catch fire.
The polyol partial esters to be used in the hydraulic base oil of the present invention have an average molecular weight (number average molecular weight) of 600 to 1,500, preferably 600 to 1000 and more preferably 650 to 950. If this molecular weight is less than 600, the hydraulic oils have the low viscosity and the low flash point and are easy to catch fire undesirably. On the other hand, if it exceeds 1,500, the hydraulic oils have the too high viscosity, undesirably susceptible to the inefficient transmission.
The kinematic viscosity is acceptable, if it is in a range good for the hydraulic oils. Ordinarily, however, it is 20 to 200 cSt, preferably 20 to 100 cSt and more preferably 40 to 80 cSt at 40xc2x0 C.
As the polyol partial esters in the viscosity range as set forth above,a trimethylolpropane diester comprising a mixture of oleic acid and isostearic acid as the fatty acid is preferably used.
The flame retardant hydraulic oils of the present invention contain the hydraulic base oils comprising the thus obtained polyol partial esters as the essential component. It is preferable that said flame retardant hydraulic oils further contain high-molecular compounds having a number average molecular weight of 10,000 to 400,000. As the high-molecular compound, a polyolefin, a polyacrylate, a polymethacrylate, a polyalkylene glycol, a polyalkylene glycol alkylether, a styrene-olefin copolymer, a styrene-maleic acid ester copolymer, a polyester and the like can be mentioned. Particularly, the polymethacrylate-based polymers or the styrene-maleic acid ester copolymers are preferably used.
The base oils are made less liable to change into a mist with hydroxyl groups, and it is said high-molecular compounds which are added thereto so that mists of base oils are even harder to develop. From this point of view, their molecular weights are preferably 10,000 to 400,000 in terms of number average molecular weight. If the molecular weights are smaller than this range, said effect can hardly be obtained undesirably. If they are larger than the range, the hydraulic oils are undesirably liable to deteriorate due to shears and lose the viscosity when they are used. It is preferable that these high-molecular compounds be contained in the hydraulic oils of the present invention in a ratio of 0.01 to 2.0% by weight. If the content of high-molecular compounds is smaller than this range, the present invention is almost ineffective undesirably. If it is too much, the deterioration due to shears is more likely to develop undesirably. If necessary, the flame retardant hydraulic oils of the present invention may as well be mixed with routinely used lubricating oil additives, such as antioxidant, extreme pressure agent, rust preventives, defoaming agent, demulsifier and the like.
Examples of the antioxidant to be used herein include a phenol-based antioxidant such as 2,6-di-t-butyl-4-methylphenol, 4,4xe2x80x2-methylenebis(2,6-di-t-butyl-4-methylphenol; an amine-based antioxidant such as N-phenyl-xcex1-napthylamine, N-phenyl-xcex2-naphthylamine, phenothiazine, monooctyldiphenylamine; or a sulfur-based antioxidant such as alkyldisulfide and benzothiazole; and a zinc dialkyldithiophosphate; and the like.
Examples of the extreme pressure agent include a zinc dialkyldithiophosphate, a dialkylpolysulfide, a triarylphosphate, a trialkylphophate and the like.
Examples of the rust preventives include an alkenyl succinate, a sorbitan monooleate, a pentaerythritol monooleate, an aminephosphate and the like.
Examples of the defoaming agent include a di-methylpolysiloxane, a diethylsilicate and the like. Examples of the demulsifier include a polyoxyalkylene glycol, a polyoxyalkylene alkylether, a polyoxyakylene alkylamide, a polyoxyalkylene fatty ester and the like.
It is preferable that the flame retardant hydraulic oils as obtained by the present invention have a biodegradability of 67% or higher as the result of biodegradation tests according to the CEC method.
The thus obtained flame retardant hydraulic oils of the present invention are excellent in the flame retardancy and unaccompanied by the dangers of pinhole fire by incorporating the hydraulic base oils comprising as the essential component the polyol partial esters, which are formed by reacting the polyols of Component (A) with the acyclic monocarboxylic acids of Component (B).
Accordingly, these flame retardant hydraulic oils can find their application, for example in various hydraulic instruments, construction machines, injection machines, machine tools, hydraulically driven robots and the like. They can also be used as an engine oil, a gear oil and an industrial lubricant for other uses
Moreover, they are biodegradable, capable of finding their application as a lubricating oil preferable from the viewpoint of environmental protection.
Now the present invention will be described in greater detail with reference to the examples which should not be construed as limiting the claimed scope of the present invention to their details.